The specification for URLClassLoader.close() states:
"In the case of jar: and file: URLs, it also closes any class files, or JAR files that were opened by it."

If a resource was got(by getResourceAsStream(...)) from resource file or jar file, this file couldn't be deleted on Windows after the call of URLClassLoader.close(). Hence the method close() doesn't close class/jar files.

Please see the following test:
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import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.URL;
import java.net.URLClassLoader;

public class UCL_minitest {
    public static void main(String[] args) throws IOException {
        final String resName = "resource.res";
        File resFile = new File(resName);
        FileOutputStream fos = new FileOutputStream(resName);
        fos.write(new byte[]{0, 1, 2, 3});
        fos.close();

        URL parentURL = resFile.getCanonicalFile().getParentFile().toURI().toURL();
        URLClassLoader loader = new URLClassLoader(new URL[] { parentURL });
        System.out.println("resource: " + loader.getResourceAsStream(resName));
        loader.close();
        System.out.println("file is successfully deleted: " + resFile.delete());
    }
}
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It's output on Solaris:
resource: java.io.BufferedInputStream@1eed786
file is successfully deleted: true

on Windows:
resource: java.io.BufferedInputStream@c3c749
file is successfully deleted: false